Diagenesis Of The Second Member Of The Xujiahe Formation In The Fenggu Area Of ​​the Western Sichuan Foreland Basin

The study of reservoir characteristics, diagenesis and diagenesis and pore evolution model of reservoir development and reservoir comprehensive evaluation of T3X2group in Fenggu area of the middlepart of western Sichuan foreland basin was intensive carried out by the means of comprehensive analysis with multidisciplinary and varying measures, guided by reservoir geology, sedimentology, Logging Geologyand seismic stratigraphy, on the basis of the data of regional geology background, outcrop, well drilling, well logging, analysis and testing, seismic and production test findings.The reservoir developed six kinds of rock types,of which the main ones are lithic quartz sandstone, lithic sandstone and felspathic lithic quartz sandstone. Interstitial material mainly include mud and adglutinate,and adglutinate mainly include clay mineral, carbonate mineral and silicoide.Of all clastic granules, mesograin is the overwhelming majority,most of which is subangularity.The granule grading is middle to good.The major reserving space type of the reservoir is secondary pore, including innerparticle dissolution pore, interparticle dissolution pore and micro fracture. The innerparticle dissolution pore contributs the most to the reservoir, interparticle dissolution pore and microfracture does less. The porosity structure is mainly the group of mesothyridid and slimsy throat. The physical property is quite poor,thus the reservoir is difined as super low porosity and low permeability reservoir.The diagenesis study is on the basis of measures of thin section analysis, SEM analysis and X-ray analysis findings. Main destructive diagenesis includes compaction, pressolution and cementation. Main constructive diagenesis includes denudation and cataclasis, and inrush of oil and gas. Metasomatism and recrystallization have little impact on reservoir pore.The relatively quality reservoir is controlled by three main factors:1.The rim cementation of ealy formed chlorite protected the primary pore.It blocked the formation of authigenic minerals in late time,released the pressure of overlying load.Moreover,it supplied fluid channels to the late dissolution.In those ways did that protect the primary porosity and favorable.2.Three denudation stages reconstruct the reservior.of which inrush of oil and gas is the key one.For lack of the soluble fraction.the overall denudation intensity is weak.However, innerparticle dissolution pores developing in an alkaline environment can be commonly found in this area.The impermeable barriers and hydrocarbons exhaust enable the secondary pore to be saved.3. Multiphasic denudation and unconformity-related differential compaction determine the degree of the microfracture.By the homogenization temperature of fluid inclusions in authigenic minerals.the maturity degree of organic matter and paleogeothermal gradient, the diagenesis evolution sequence of the reservoirs habe been built. The sandstone of this area has been in the middle diagenetic stage B, and the reservoir space experienced three stages:the destruction of primary porosity caused by the compaction in the early diagenetic stage;secondary porosity created by acidic water dissolution in the middle diagenetic stage A,when the oil and gas poured into the reservoirs;and the destruction of secondary porosity caused by the cementation of carbonate cements and siliceous in the subsequent diagenetic stages.This area has two diagenesis patterns:early denudation-early differential compaction-late denudation; rim cementation of ealy formed chlorite-early denudation-late denudation.